Is naishthika brahmacharya (life-long celibacy) essential as a sadhana for Self-Realisation?
Realisation itself is naishthika brahmacharya. The vow is not brahmacharya. Life in Brahman is brahmacharya and it is not a forcible attempt at it.
To live and move in Brahman is real brahmacharya; continence, of course, is very helpful and indispensable to achieve that end. But so long as you identify yourself with the body, you could never escape sex-thought and distraction. It is only when you realise that you are formless Pure Awareness that sex-distinction disappears for good and that is brahmacharya, effortless and spontaneous.
It is said that kama (desire), krodha (anger), etc.. vanish in the presence of the Sadguru. Is it so?
It is correct. Kama and krodha must vanish before Self-Realisation.
1) Talk 491
Om Namo Bhagavate Sri Ramanaya!